An excimer laser apparatus usually must be equipped with gas containers for replacing laser medium gases. Laser medium gases that are required are a rare gas (krypton, xenon, and the like), a halogen gas (fluorine, hydrogen chloride, and the like), and a buffer gas (neon, helium, and the like). When an excimer laser is used in ordinary industrial applications, the full replacement of the laser medium gases is performed from about once daily to about once every three days, with several hundred liters (calculated at atmospheric pressure) of gas being consumed each time. The gases are usually supplied from gas containers which have a capacity of 3 to 47 liters and a charge pressure of 20 to 150 kgf/cm.sup.2.
The price of the gas per unit of volume is generally lower for a greater volume of gas that can be charged into one container, and a larger container also requires less frequent replacement work. Accordingly, with a conventional excimer laser apparatus, the gas containers were set up together in one place somewhere away from the laser apparatus, and the gases were supplied to the laser apparatus through gas piping.
Furthermore, halogen gases, which are one of the laser medium gases, are extremely toxic, and various safety measures must therefore be implemented. Consequently, in the past the container used for the halogen gas was stored in a container cabinet, inside of which was forcibly ventilated. The exhaust air was released into the atmosphere only after it was purified with exhaust gas treatment equipment (hereinafter referred to as a scrubber). In addition, the inside of the cabinet was furnished with a gas leakage detector, a container cock emergency shutoff valve, and so on.
However, since the gas containers were set up together in one place somewhere away from the laser apparatus with such a conventional apparatus, the gas supply and treatment system aside from the laser apparatus itself, such as the gas container stand, the cabinet, the gas piping, and the scrubber, ended up being quite large. An arrangement such as this was advantageous in terms of costs and the management of the containers when gas was supplied to numerous laser apparatuses, but when only a few laser apparatuses were involved, this setup was unsatisfactory from the standpoints of cost and layout.
Moreover, installation restrictions in factories and the like sometimes require that the piping carrying the fluorine, chlorine, and other reactive gases will extend for dozens of meters, which means that the inner surface area of the piping is very large, which is a drawback in that the admixture of impurities or particles into the laser gas can result in unstable laser performance.
There were also cases in which the container cabinet was positioned beneath the laser apparatus, but since this meant that a 47-liter container had to be laid on its side, the work of replacing the container was extremely difficult. Furthermore, the laser apparatus and the laser cabinet are constructed by separate units in this case, and the gas piping used to connect the two was exposed on the outside, so there was no protection against some kind of object bumping into this piping and causing a leak, and this constituted a safety problem. Also, this prior art was not designed so that the work involved during replacement could be carried out on one side of the laser apparatus, so work space had to be allocated all the way around the cabinet, which was a drawback in that the laser apparatus took up more floor space.
Finally, setting up the laser apparatuses and the container cabinet separately when only a few laser apparatuses were to be used resulted in extremely high costs for the container cabinet and gas piping.
The present invention was conceived in light of this situation, and an object thereof is to provide an inexpensive laser apparatus that is easy to maintain and whose laser performance is highly stable.